AQA GCSE Science PHYSICS 3 Unit P3.2 Using physics to make things work

• Know and understand that many things, from simple toys to complex fairground rides, are constructed from basic machines such as the lever.

• Appreciate that a knowledge of the physics involved in balancing and turning can help us to make these appliances work.

• You should be able to use your skills, knowledge and understanding to:

  • analyse the stability of objects by evaluating their tendency to topple,

    • You may have used a range of laboratory equipment to model real-life situations, eg cranes,

  • recognise the factors that affect the stability of an object,

    • You should recognise that objects with a wide base and low centre of mass are more stable than those with a narrow base and a high centre of mass,

  • evaluate how the design of objects affects their stability,

  • interpret and evaluate data on objects moving in circular paths,

    • You should understand that a centripetal force does not exist in its own right but is always provided by something else such as gravitational force, friction or tension.

AQA GCSE Science PHYSICS Unit P3.2.1 Centre of mass

• a) Know and understand that the centre of mass of an object is that point at which the mass of the object may be thought to be concentrated.

  • You will be expected to be able to describe how to find the centre of mass of a thin, irregular sheet of a material.

• b) Know and understand that if freely suspended, an object will come to rest with its centre of mass directly below the point of suspension.

• c) Know the centre of mass of a symmetrical object is along the axis of symmetry.

• d) Know that for a simple pendulum:

  • and be able to use the formula:

  • T = 1/ f

  • T is periodic time in seconds, s

  • f is frequency in hertz, Hz

    • Know that applications of the pendulum should include simple fairground and playground rides.

    • The equation T = 2∏√(l/g) is not required.

• e) Know that the time period depends on the length of a pendulum.

AQA GCSE Science PHYSICS Unit P3.2.2 Moments

• a) Know that the turning effect of a force is called the moment.

• b) Know that the size of the moment is given by the equation:

  • M = F x d

  • M is the moment of the force in newton-metres, Nm

  • F is the force in newtons, N

  • d is the perpendicular distance from the line of action of the force to the pivot in metres, m

• c) Know and understand that if an object is not turning, the total clockwise moment must be exactly balanced by the total anticlockwise moment about any pivot.

• d) HT only: Be able to calculation of the size of a force, or its distance from pivot, acting on an object that is balanced.

• e) Appreciate the idea of simple levers limited to levers as force multipliers.

• f) HT only: Know and understand that if the line of action of the weight of an object lies outside the base of the object there will be a resultant moment and the body will tend to topple.

  • HT only: Your knowledge of applications should include vehicles and simple balancing toys.

AQA GCSE Science PHYSICS Unit P3.2.3 Hydraulics

• a) Know and understand that liquids are virtually incompressible, and the pressure in a liquid is transmitted equally in all directions.

  • You should understand that this means that a force exerted at one point on a liquid will be transmitted to other points in the liquid.

• b) Know and understand that the use of different cross-sectional areas on the effort and load side of a hydraulic system enables the system to be used as a force multiplier.

• c) Know that the pressure in different parts of a hydraulic system is given by:

  • P = F / A

  • P is the pressure in pascals, Pa

  • F is the force in newtons, N

  • A is the cross-sectional area in metres squared, m²

AQA GCSE Science PHYSICS Unit P3.2.4 Circular motion

• a) Know and understand that when an object moves in a circle it continuously accelerates towards the centre of the circle.

  • Know that this acceleration changes the direction of motion of the body, not its speed.

• b) Know and understand that the resultant force causing this acceleration is called the centripetal force and is always directed towards the centre of the circle.

  • You should be able to identify which force(s) provide(s) the centripetal force in a given situation.

• c) Know and understand that the centripetal force needed to make an object perform circular motion increases as:

  • the mass of the object increases,

  • the speed of the object increases,

  • the radius of the circle decreases,

    •  The equation F = mv² / r is not required.

• Practical work in unit 3.2 to help develop your skills and understanding may have included the following:

  • demonstrating that pressure in liquids acts in all directions using a circular container with holes around it

  • finding the centre of mass of an irregularly shaped card

  • using a balanced metre ruler and masses to verify the principle of moments

  • planning and carrying out an investigation into factors that affect the period of a simple pendulum (mass, length of pendulum, amplitude of swing)

  • whirling a bung on the end of a piece of string to demonstrate the factors that affect centripetal force

  • investigating objects and slopes to find out the point at which the object topples.